Corrosion inhibitors



United States Patent 3,281,281 CORROSION INHIBITORS Hugh F. Schaefer,Lakewood, Ohio, assignor to Union Carbide Corporation, a corporation ofNew York No Drawing. Filed Oct. 28, 1963, Ser. No. 319,577 7 Claims.(Cl. 136107) This invention relates to the inhibition of corrosion ofzinc and it more particularly refers to the inhibition of corrosion ofzinc in alkaline environment and to the prevention of the formation ofexcessive amount of gas in alkaline galvanic cells.

Zinc has been the most common anode material for galvanic cells for manyyears. In the past few years galvanic cells which utilize an alkalineelectrolyte have gained prominence for many applications. It has beenfound that there is a certain amount of corrosion of the zinc anode inthese cells which is not productive of useful electric power. Very oftenthis corrosion occurs When the cell is in storage, and this, of course,tends to reduce the effective life of the cell when it is finally put inservice.

A solution has been proposed for this problem which is based upon thesaturation or near saturation of the electrolyte with products of zinccorrosion thu putting the system in equilibrium with respect to zinccorrosion. This has been accomplished by adding zinc oxide or zincateions to the electrolyte. It has also been found that the amalgamation ofthe zinc anode very often aids in the inhibition of non-productivecorrosion by electrolyte. These proposals have worked Well; however, itis desirable to have alternate materials which are effective bythemselves to inhibit zinc corrosion.

It is a primary object of this invention to provide materials whichinhibit the corrosion of zinc in alkaline environment.

It is another primary object to prevent the formation of large volumesof gas within a zinc cell and thus preserve the structural integrity ofthe cell.

It is a more particular object to inhibit the nonproductive corrosion ofZinc anodes in alkaline galvanic cells.

It is another object to improve the characteristics of alkaline galvaniccells having zinc anodes.

This invention i based upon the discovery that there are certain organiccompounds which prevent the corrosion of zinc in alkaline environmentwithout relying on the establishment of equilibrium conditions betweenzinc, alkali, and zinc corrosion products.

In accord with this invention and the above stated objects, theinhibition of the corrosion of zinc is accomplished by the presence ofan inhibiting amount of N,N-diethylcarbanilide. This compound ischaracterized by the fact that it is: substantially passive to theelectrochemical reaction between zinc and an alkaline environment,chemically inert to both zinc and the alkaline environment, andresistant to oxidation.

It has been found that this compound inhibits the corrosion of zinc inboth the solid form and in the powdered form. This inhibitor does notinterfere with the normal operation of the zinc as an electrode and yetis effective to inhibit non-productive corrosion of the zinc, and toreduce gassing associated therewith.

The term corrosion, refer to non-productive corrosion of the zinc anodewhich does not produce a usable galvanic current, unless otherwiseindicated.

The above described corrosion inhibitor is effective when used with bothamalgamated zinc and non-amalgamated zinc. The corrosion of amalgamatedzinc, which is normally less subject to corrosion than nonamalgamatedzinc, is inhibited to a greater degree by the 3,281,281 Patented Oct.25, 1966 presence of the herein described inhibitor. The corrosioninhibiting character of N,N-diethylcarbanilide has been found to besubstantially stable and does not diminish appreciably with the passageof time under normal storage and operating conditions.

The inhibitor compound can be incorporated in the cell in several ways.For example, the selected inhibitor can be added directly to theelectrolyte prior to gelling the electrolyte. Alternatively theinhibitor can be dissolved in a suitable solvent, e.g., acetone, and thepowdered zinc anode material then soaked in the solution. The solvent isthen evaporated and the treated zinc incorporated in the cell. Asanother method the inhibitor solution can be sprayed into the anodematerial. For use in galvanic cells it is preferred to add the corrosioninhibitor to the anode material. In any event a homogeneous distributionof the inhibitor is desirable to provide uniform protection.

The compound described is employed in an inhibiting amount, that is, anamount which is sufficient to inhibit or substantially prevent theoccurrence of non-productive corrosion and the formation of gas. Ingeneral, amounts of about 0.01 to about 1.0 weight percent based on theweight of anode material to be protected, i.e., on the weight of zinc,provide satisfactory corrosion inhibition. The actual amount ofinhibitor necessary to provide adequate inhibition in any particularsituation can easily be determined by methods well known in the art.

In order to test the simple corrosion inhibition effects of thiscompound in alkaline environment with respect to zinc, a mixture of 0.1to 0.5 weight percent of the compound in a 30 percent aqueou solution ofpotassium hydroxide was made. A strip of zinc having a surface area of6.15 square centimeters which weighed about 2 grams was immersed in eachmixture. Table I below is a compilation of data taken from these testsshowing the weight loss of each strip, given in milligrams, after aspecific immersion time, given in days. These tests were run at 21 C.and 45 C. and the results at both temperatures are reported.

TABLE I Inhibitor Wt. loss Time Wt. loss Time s) y a) (days) These datadramatically show the effect of the compound of this invention on zinccorrosion in alkali environment. Table II below shows the improvedcorrosion resistance afforded by this compound in alkaline solutionwhere the zinc has been amalgamated previous to immersion with 2.1weight percent mercury. The data herein shown were taken at 45 C. andare reported as weight loss in milligrams after a specific immersiontime given in days.

TABLE II Inhibitor Wt. loss Time N one 1 83 341 224 719 10-14 196-217 1Other than mercury.

of sealed cells would be expected with the use of this compound. Thiscompound is also expected to be beneficial with respect to corrosion andgassing under considerably less stringent conditions, e.g., duringstorage of fresh cells.

TABLE III Voltage of Fresh Cells Voltage of 50 percent AdditiveDischarged Cells Gassnig of Discharged Open Closed Open Closed CircuitCircuit Circuit Circuit (1.0 amp.) (1.0 amp.)

None 1. 48-1. 53 1. 37-1. 46 1. 24-1. 28 0. 94-1. 12 Excessive inmajority of cells:

cell rupture observed in several cases even after 1 month andparticularly after 6 months at ambient room temperature.N,N-diethylcarbanilide 1. 46-1. 51 1. 36-1. 40 1.29-1.31 1. 06-1.Substantial reduction of gassing even after 6 months at ambient roomtemperature.

and above the reduction effected by the amalgamation of the Zinc. Thus,it is seen that N,N-diethylcarbanilide acts as a corrosion inhibitor forzinc in alkaline environment and actually improves the performance ofcertain conventional corrosion inhibitors.

To further illustrate the advantageous characteristics ofN,N-diethylcarbanilide, standard D-size alkalinemanganes'e dioxide cellswere prepared. Powdered zinc, which was amalgamated to the extent ofabout 4 percent by weight was immersed for about 24 hours in a solutioncontaining one percent N,N-diethylcarbanilide based on the Weight ofamalgamated zinc. The solvent was then thoroughly evaporated in a vacuumoven at between 40 C. and 60 C. The thus-treated zinc was thenincorporated in standard alkalinemanganese dioxide cells employingpotassium hydroxide as the electrolyte.

Table III shows the voltage characteristics of cells containing thetreated anodes. Both open circuit potentials and those on a one-ampereload (by the interrupter technique) were observed. Substantially noeffect on cell performance was noted.

These cells were then discharged at 0.5 to 1.0 ampere continuous drainto approximately percent of their capacity. Open and closed circuitvoltages of the used cells were then recorded. The range of voltages ofthe treated cells was approximately the same as the ranges observed incontrol cells, thus again indicating little or no effect of theadditives on cell performance. This particular test is believed to be avery severe one in that about 90 percent of control cells, sodischarged, showedexcessive gassing and, in many cases, actual ruptureof the cell containers occurred. After 50 percent discharge, a series oftreated and control cell were connected to mercury manometers to measuregas pressure build-up over a period of 1 to- 6 months at ambient roomtemperature. As Table III shows, the gassing was substantially reducedin the cells containing the inhibitor compound of this invention. Thusno rupture What is claimed is:

1. A method of inhibiting corrosion of zinc exposed to an alkalineenvironment which comprise effecting said exposure in the presence of acorrosion inhibitor comprising N,N-diethylcarbanilide.

2. The method of claim. 1 wherein said alkaline environment comprises.01 to 1.0 weight percent, based on the Weight of said zinc, of saidN,N-diethylcarbanilide.

3. The method of claim 1 wherein said alkaline environment is an aqueoussolution of potassium hydroxide.

4. The method of claim 1. wherein said zinc is amalgamated.

5. A galvanic cell comprising a zinc anode, a cathode depolarizer, andalkaline electrolyte and N,N-diethylcarbanilide in an inhibiting amount.

6. The galvanic cell described in claim 5 wherein the corrosioninhibiting amount is from about 0.01 to about 1.0 weight percent basedon the Weight of the zinc anode.

7. The galvanic cell described in claim 6 wherein said electrolyte is anaqueous solution of potassium hydroxide and said cathode depolarizer ismanganese dioxide.

References Cited by the Examiner UNITED STATES PATENTS 2,829,114 4/1958Hervert 252-387 X 2,897,250 7/1959 Klopp 136-107 2,900,434 8/1959Zimmerman et al. 136-107 X 3,095,331 6/1963 Davis 136-107 OTHERREFERENCES Morehouse et al., EiTect of Inhibitors on the Corrosion ofZinc in Dry-Cell Electrolytes, Journal of Research of the NationalBureau of Standards, vol. 40, 1948, pps. 151-161.

WINSTON A. DOUGLAS, Primary Examiner. ALLEN B. CURTIS, Examiner.

D. L. WALTON, Assistant Examiner.

1. A METHOD OF INHIBITING CORROSION OF ZINC EXPOSED TO AN ALKALINEENVIRONMENT WHICH COMPRISES EFFECTING SAID EXPOSURE IN THE PRESENCE OF ACORROSION INHIBOTOR COMPRISING N,N-DETHYLCARBANILIDE,: